Goldsmith told Popular Science: "Interceptor use in the U.S. is much higher than people had anticipated. One of our customers took a road trip from Florida to North Carolina and he found eight different interceptors on that trip. We even found one at South Point Casino in Las Vegas.”

The towers were found in July, but the report implied that there may have been more out there.

Although it is unclear who owns the towers, ESD found that several of them were located near U.S. military bases.

"Whose interceptor is it? Who are they, that's listening to calls around military bases? Is it just the U.S. military, or are they foreign governments doing it? The point is: we don't really know whose they are," Goldsmith said to Popular Science.